This invention relates to a device for recording and/or reading binary data on both faces of a flexible magnetic disk, which may be contained in a cardboard or plastics sleeve. The magnetic disk is normally constituted by a thin plastics sheet coated on both sides with a layer of magnetisable material, and can rotate inside its sleeve by virtue of the presence of a lubricating material. The sleeve has a central through hole via which access can be gained to the magnetic disk from both sides in order to rotate it by drive means. The faces of the sleeve are provided with a pair of opposed slots disposed radially relative to the disk, through which access can be gained to the disk by means of the magnetic recording and/or reading heads.
Before bringing the magnetic heads into contact with the disk faces, the sleeve is urged by a presser against a fixed reference surface, in order to flatten the sleeve in a zone close to its radial slots, and thus position the disk in a nominal working plane.
A recording and/or reading device is known in which two arms disposed on opposite sides of the disk are pivoted to a carriage mobile radially along the axis of the sleeve slots, and are both movable between a rest position, in which they are spaced well away from the magnetisable surfaces of the disk, and a working position in which they are in proximity to the disk. A magnetic head is mounted by means of a very yieldable spring at the end of each arm, and can rotate in all directions about a central support. During reading and/or recording operations, the two opposing heads are kept in contact with the disk faces by means of a very small load, of about 8 grams. Because of this and the great yieldability of their springs, the magnetic heads are in theory free to follow every oscillation of the disk during its rotation, and can also move along an axis perpendicular to the plane of the disk, if this latter becomes disposed in a plane other than its nominal plane of rotation.
Beside requiring high precision in tests of its assembly and its setting in the apparatus in which it is mounted, this device has the drawback of causing excessive wear of the disk, in particular during the stage in which the heads "land" on the magnetised surfaces, and of providing very inconstant contact between the magnetic heads and the disk, and as a consequence a signal which is of non-uniform amplitude.
In another known device, the lower magnetic head is fixed on to the carriage, and its surface which makes contact with the disk is perfectly flat in order to define a reference surface against which the disk rests with its lower face.
The lower head is positioned on the carriage in such a manner that its flat surface is always above the nominal plane of rotation of the disk so that, during operation, the head "penetrates" into the disk, deforming it locally. A load of about 18 grams is applied to the upper head, which is of the type in the device described heretofore, and this tends to flatten the disk zone between the heads against the flat surface of the lower head. The lower head is therefore in an absolutely fixed position relative to the direction normal to the plane of the disk. Moreover, the disk can become positioned in planes other than the nominal plane because of the sleeve tolerances, and the tolerances of the entire recording and/or reading apparatus. The consequence is that this latter device has the drawback of very variable local deformation of the disk. Under marginal apparatus and disk conditions, due to variations in their friction coefficient and sleeve thicknesses, this causes inconstant head-disk contact, and a signal of non-uniform amplitude. Moreover, when this local deformation reaches the upper limiting level, there is considerable wear of the disk during its rotation.